Project 5 - Intensive glycemic control is now recommended as the standard of care for all patients with diabetes. Unfortunately, the major barrier to achieving euglycemia in patients with diabetes is hypoglycemia. Further complicating management of patients with diabetes is that the therapeutic cornerstone of exercise also,contributes to increased hypoglycemia. Many studies have identified that intensive glycemic control can result in acquired failure of neuroendocrine and importantly autonomic nervous system(ANS) counterregulatory responses during hypoglycemia. Recent work has also demonstrated that episodes of both antecedent hypoglycemia and exercise can result in reciprocal, subsequent ANS counterregulatory dysfunction during either stress. The mechanisms responsible for prior hypoglycemia and/or exercise resulting in ANS counterregulatory dysfunction have yet to be determined. Recent interest has begun to be Focused on central nervous system (CNS) regulation of physiologic responses during exercise and hypoglycemia. It is known that brain corticosteroid and GABAA receptors are powerful inhibitors of ANS and neuroendocrine function. We hypothesize that prior activation of GABAA and/or corticosteroid (type 1 MR and/or type 2 GR) receptors are mechanisms responsible for the hypoglycemia induced ANS counterregulatory dysfunction occurring during exercise. Currently, there are no adjunct treatments that protect the ANS from the deleterious effects of repeated episodes of hypoglycemia. In this application, we will propose therapeutic interventions aimed at reversing the central mechanisms that result in hypoglycemia associated autonomic dysfunction (HAAD). We have preliminary data that six weeks administration of the selective serotonin receptor inhibitor, fluoxetine, can increase ANS, neuroendocrine and metabolic (glucose <inetics, lipolysis) responses to hypoglycemia in healthy individuals. Whether these novel findings will apply to patients with type 2 diabetes (T2DM) is unknown. We will also hypothesize that targeted inhibition of norepinephrine transporters will prevent the development of HAAD. The studies outlined in this proposal are :herefore focused at determining the in-vivo mechanisms regulating ANS counterregulatory failure during lypoglycemia and exercise in healthy and diabetic humans. Experiments will use the glucose clamp echnique. ANS responses to hypoglycemia will be assessed by measuring circulating catecholamines, pancreatic polypeptide, muscle sympathetic nerve activity (MSNA), symptom scores and heart rate /ariability. Neuroendocrine responses will be determined by measuring growth hormone, cortisol and ACTH. Metabolic counterregulatory mechanisms will be quantified by measuring glucose and glycerol turnover, substrate levels, and substrate oxidation via indirect calorimetry. The specific aims of this proposal are to determine: 1) the roles played by GABAA and corticosteroid receptors in the development of hypoglycemia related exercise associated autonomic dysfunction, 2) if selective serotonin reuptake inhibitors can increase ANS and neuroendocrine counterregulatory responses to hypoglycemia in T2DM, and 3) if inhibition of )resynaptic norepinephrine transport can prevent HAAD in healthy man. ^___